In recent years, there has been a surge of interest in exploiting biosensing systems based on CMOS-compatible silicon nanowire field-effect transistors (NWFETs) (Stern et al., 2008, IEEE Trans. Electron Devices, 55: 3119-3130; Curreli et al., 2008, IEEE Trans. Nanotechnol., 7: 651-667; Elfstrom et al., 2008, Nano Lett., 8: 945-949; Gao et al., 2011, Nano Lett., 11: 3974-3978). Silicon nanowires (Si-NWs) modified with specific surface receptors present a powerful detection platform for a broad range of biological and chemical species. The small diameter of NWFET devices provides extremely high sensitivity because the binding of target molecules causes accumulation/depletion of carriers throughout the wire cross-section, enabling label-free, real-time detection and monitoring of biomolecular interactions (Park et al., 2007, Biosens. Bioelectron., 22: 2065-2070; Bunimovich et al., 2006, J. Am. Chem. Soc., 128: 16323-16331; Zheng et al., 2005, Nat. Biotechnol., 23: 1294-1301; Hakim et al., 2012, Nano Lett., 12: 1868-1872; Duan et al., 2012, Nat. Nanotechnol., 7: 401-407; Ishikawa et al., 2009, ACS Nano, 3: 1219-1224; Cui et al., 2001, Science, 291: 851-853; Stern et al., 2007, Nature, 445: 519-522; Gong, 2010, Small, 6: 967-973; Lee et al., 2010, Nanomedicine, 6: 78-83). Although such devices were first demonstrated by chemically synthesized VLS NWs (Cui et al., 2001, Science, 291: 851-853), top-down fabricated CMOS-compatible Si-NW devices offer advantages of high yield, exceptional uniformity, and system-level integration and multiplexing (Steprn et al., 2007, Nature, 445: 519-522). Within the past few years, many of the previous limitations to charge-based affinity sensors, such as charge screening and sensor drift, have been solved (Steprn et al., 2010, Nat. Nanotechnol., 5: 138-142; Fritz et al., 2002, Proc. Natl. Acad. Sci. U.S.A., 99: 14142-14146; Milovic et al., 2006, Proc. Natl. Acad. Sci. U.S.A., 103: 13374-13379). In addition, the ability to multiplex electronic sensors for higher accuracy and false positive/negative elimination has become an attractive benefit of the approach. NWFETs not only represent an attractive technology for future miniaturized and multiplexed biosensing platforms but could also be extended to high-throughput functional assays (e.g., drug screening).
In order to detect bimolecular interactions, receptor molecules (e.g., proteins or protein-binding ligands) are immobilized on the Si NWFET surface, and the target (bio)molecules are recognized through specific binding. The performance of biosensors, specifically the sensitivity, specificity, reusability, chemical stability, and reproducibility, is critically dependent on the (bio)functionalization of the sensor platform. The type of linkers used for the immobilization of the capture probes and the exact immobilization protocols play a vital role in the overall performance of sensors (Jonkheijm et al., 2008, Angew. Chem., Int. Ed., 47: 9618-9647). Currently, the commonly used strategy for immobilization is attaching the receptor molecules to the nanowire surface via a covalent approach through amino silanization of the Si/SiO2 surface, followed by amine coupling (Gao et al., 2011, Nano Lett., 11: 3974-3978; Nicu et al., 2008, J. Appl. Phys., 104: 111101-111116). Such covalent attachment has disadvantages, such as autoxidation of amine-functionalized surfaces, which could limit long-term device application, lack of control of molecule placement and conformation (with a potential reduction in activity), and increasing heterogeneity in the population of immobilized species. Most importantly, such attachment is irreversible, and functionalized devices can be (practically) used only once, an issue that has limited this approach for applications.
Thus, there is a need in the art for sensor systems and devices with improved probe immobilization. The present invention satisfies this unmet need.